Heretofore, various methods have been proposed as methods for producing dichloropentafluoropropane (HCFC-225) represented by a chemical formula C3HCl2F5. For example, a method has been proposed which comprises contacting dichlorofluoromethane with tetrafluoroethylene in the presence of a modified aluminum chloride catalyst to obtain dichloropentafluoropropane, and a technique to apply isomerization to a mixture of various isomers of dichloropentafluoropropane obtained by this method, is disclosed (Patent Document 1).
However, by the isomerization method disclosed in Patent Document 1, it was not possible to obtain 1,1-dichloro-2,2,3,3,3-pentafluoropropane (HCFC-225ca) at a high content ratio.
On the other hand, in recent years, it has been studied to use 2,3,3,3-tetrafluoropropene (R1234yf) having a small ozone depletion potential, as a cooling medium of next generation to be substituted for 1,1,1,2-tetrafluoroethane (HFC-134a) being a greenhouse gas. It is considered to use 1,1-dichloro-2,3,3,3-tetrafluoropropene (R1214ya) as a starting material for preparing this R1234yf, and accordingly, usefulness of HCFC-225ca is expected as a starting material to obtain R1214ya. However, a method has not yet been found whereby HCFC-225ca can be efficiently obtained by increasing the content ratio of HCFC-225ca in the mixture of various isomers of HCFC-225.    Patent Document 1: U.S. Pat. No. 5,157,171.